Some male bettas are more aggressive than others. Some love having company of other fish and some hate it. In the wild they are loners until it comes time to breed. I would get him his own tank because it doesn't sound like he's very happy.

Thanks for the suggestions. I got rid of the balloon mollies. =[ I felt so bad the guy just dumped em in the tank without floating i wanted to smack him in the face.... he was the owner of the store. I don't wanna go there anymore now. Considering how he treated my fish. anyways... ya I had too many fish so I moved some to the 10g I was thinking of giving them away anyways. Still feel guilty tho! :( But so he's lone. I might find a way to separate the tank though. I originally planned to use that tank as a maternity tank for my female fishies to give birth in and still would like to use it for that.

Unfortunately 99.9% of fish store employees could care less about the fish. It aggravates the crap out of me! Don't feel guilty, hopefully they'll end up going to good homes. You can divide the tank and put another male or female into the tank. You could even divide it three ways so each fish has 3Gs. You could also put 4 or 5 female bettas in called a female sorority and put the male in a separate tank. Males and females should never be in the same tank together unless you're breeding them or the tank is divided.

What type of female fish would you want to use it for to give birth in? If you're talking about female bettas, it doesn't work like that. You have to breed a pair separately and even that is risky. The male could kill the female or the female could kill the male.